Myriad approaches have been pursued to control pests. Many of these approaches are directed to the control of pests that attack plants, most notably commercially valuable plants. Although much current agricultural research has pest control as its objective, pest destruction of plants and plant products is still a major problem.
Chemical pesticides in particular have been used extensively to control pests for many years. An awareness of recent problems associated with the use of chemical pesticides such as adverse effects on man and the environment has led to a focus on biological control alternatives to chemical pesticides. For instance, certain fungi have been identified to be pathogenic to different pests. Importantly, many fungi, unlike pathogenic bacteria, viruses and protozoa need not necessarily be ingested by the target insect to initiate disease, but instead usually invade through their host's cuticle.
Sweetpotato whitefly is a particularly serious insect pest worldwide. In Texas and California alone, agronomic losses exceed $250 million annually. The insect rapidly develops resistance to chemical pesticides and is not adequately controlled with current pest management practices.
Various strains of the fungus Paecilomyces fumosoroseus have been proposed as a possible biological control agent for sweetpotato whitefly. A significant constraint to the development of this fungus and other like fungi as biocontrol agents, however, is the availability of low-cost methods for producing infective propagules. Solid-substrate methods of producing spores from such fungi as Paecilomyces fumosoroseus have proven too costly for commercial consideration. Hence, liquid culture methods for producing spores are preferred.
Eyal et al. has described in U.S. Pat. No. 5,360,607 a submerged culture technique for growing the mycelium of Paecilomyces fumosoroseus. The grown mycelial biomass is harvested and then formed into dry prill which can be used directly on plants and soil or the prill can be used as a carrier for sporulation of conidia spores. However, to be an effective insecticidal agent, mycelia containing prill must be wetted, the fungus must grow and sporulate, and insects must contact the newly formed spores. It would be more advantageous to develop a method of producing a high volume of insecticidal spores (versus mycelium) which could be directly applied to insects and actively instigate insect kill without the need for sporulation and contact by the target insect.
Previous attempts to produce Paecilomyces fumosoroseus spores directly using liquid culture fermentation methods have yielded unstable spores which are desiccation intolerant and hence readily perish during drying. Clearly, there is a need to develop a method to rapidly produce high volumes of spores which are desiccation tolerant and have high survival rates after drying and storage. In particular, it would be useful to produce desiccation tolerant spores of Paecilomyces fumosoroseus.